The present invention relates generally to phase change materials. More particularly, the present invention relates to stabilized phase change materials and methods of stabilizing phase change materials that are useful in the manufacture of melt spun synthetic fibers.
Many fabric materials are made from synthetic fibers. While the spirit and scope of this invention is not to be limited to the following definition, a fiber is typically considered to have a length several times (e.g., 100 times or more) greater than its diameter. Conventionally, two processes are used to manufacture synthetic fibers: a wet solution process and a melt spinning process. The wet solution process is generally used to form acrylic fibers, while the melt spinning process is generally used to form nylon fibers, polyester fibers, polypropylene fibers, and other similar type fibers. As is well known, a nylon fiber comprises a long-chain synthetic polyamide polymer characterized by the presence of an amide group xe2x80x94CONHxe2x80x94, a polyester fiber comprises a long-chain synthetic polymer having at least 85 percent by weight of an ester of a substituted aromatic carboxylic acid unit, and a polypropylene fiber comprises a long-chain synthetic crystalline polymer having at least 85 percent by weight of an olefin unit and typically having a molecular weight of about 40,000 or more.
The melt spinning process is of particular interest since a large portion of the synthetic fibers that are used in the textile industry are manufactured by this technique. The melt spinning process generally involves passing a melted polymeric material through a device that is known as a spinneret to thereby form a plurality of individual synthetic fibers. Once formed, the synthetic fibers may be collected into a strand or made into a cut staple. The synthetic fibers can be used to make woven or non-woven fabric materials, or alternatively, the synthetic fibers can be wound into a yarn to be used thereafter in a weaving or a knitting process to form a synthetic fabric material.
Phase change materials have been incorporated into acrylic fibers to provide enhanced reversible thermal properties to the fibers themselves as well as to fabric materials made therefrom. This is readily accomplished, in part due to the high levels of volatile materials (e.g., solvents) typically associated with the wet solution process of forming acrylic fibers. However, it is more problematic to incorporate phase change materials into melt spun synthetic fibers. During a melt spinning process, temperatures involved are typically in the range of from about 200xc2x0 C. to about 380xc2x0 C., and pressures encountered may be as high as 3000 pounds per square inch. Such processing conditions may induce degradation of the phase change materials and thus may lead to inadequate levels of thermal regulating properties normally associated with use of the phase change materials.
At elevated temperatures or pressures, certain phase change materials such as, for example, paraffinic hydrocarbons and waxes may undergo thermally induced decomposition or isomerization. Factors affecting the extent and nature of thermally induced decomposition and isomerization include magnitude of temperature, pressure, and duration of time during which a phase change material is subjected to elevated temperatures or pressures. For paraffinic hydrocarbons at a temperature of about 350xc2x0 C., thermally induced decomposition may lead to formation of lower molecular weight products (e.g., gaseous products), and thermally induced isomerization may lead to formation of branched-chain alkanes. Accordingly, a lesser amount of an unreacted paraffinic hydrocarbon may remain to effectively provide a thermal regulating property. Moreover, products resulting from thermally induced decomposition or isomerization may act as impurities. For example, a magnitude of a paraffinic hydrocarbon""s latent heat of fusion may depend on the purity of the paraffinic hydrocarbon and on the ability of the paraffinic hydrocarbon to crystallize fully. Impurities resulting from thermally induced decomposition or isomerization may hinder crystallization of a remaining unreacted paraffinic hydrocarbon to further reduce its effectiveness.
Alternatively or in conjunction with thermally induced decomposition or isomerization, certain phase change materials may undergo oxidation at elevated temperatures or pressures. For example, paraffinic hydrocarbons may undergo significant oxidation in the presence of atmospheric oxygen at temperatures as low as about 80xc2x0 C. to about 120xc2x0 C. Oxidation may lead to a lesser amount of an unreacted phase change material remaining to effectively provide a thermal regulating property. Moreover, products resulting from oxidation of the phase change material may act as impurities to further reduce effectiveness of the phase change material. For example, oxidation of paraffinic hydrocarbons may lead to formation of organic products such as, for example, esters, alcohols, aldehydes, acids, peroxides, or water. The presence of impurities can lower the latent heat and adversely affect a thermal regulating property provided by a phase change material and by a synthetic fiber or fabric material in which the phase change material is incorporated.
When a phase change material is degraded as a result of elevated temperatures or pressures, the melt spinning process itself can be adversely affected. In particular, products resulting from thermally induced decomposition, thermally induced isomerization, or oxidation of the phase change material may react with a fiber-grade thermoplastic polymer and lead to degradation (e.g., weakening or discoloration) of the polymer itself and of a resulting synthetic fiber.
It is against this background that a need arose to develop stabilized phase change materials that would be useful in the manufacture of melt spun synthetic fibers.
In one innovative aspect, the present invention relates to a stabilized phase change composition. In one exemplary embodiment, the stabilized phase change composition may comprise a phase change material and a stabilizing agent selected from the group consisting of antioxidants and thermal stabilizers.
In another innovative aspect, the present invention relates to an encapsulated phase change material. In one exemplary embodiment, the encapsulated phase change material may comprise a hollow shell defining an internal cavity and a phase change composition positioned in the internal cavity, wherein the phase change composition comprises a phase change material and a stabilizing agent selected from the group consisting of antioxidants and thermal stabilizers.
In another exemplary embodiment, the encapsulated phase change material may comprise a hollow shell defining an internal cavity, wherein the hollow shell comprises a base material and a stabilizing agent dispersed within the base material, and the stabilizing agent is selected from the group consisting of antioxidants and thermal stabilizers. The encapsulated phase change material may further comprise a phase change material positioned in the internal cavity.